The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
In general, upsetting is one of processing performed by applying pressure to a raw material in the axial direction thereof to thereby enlarge a diameter of a predetermined portion of the raw material. An improvement of such upsetting is known by Japanese Unexamined Laid-open Patent Publication No. 48-62646 (see pages 1 and 2, FIGS. 1 to 4).
In the conventional upsetting method, in cases where an enlarged diameter portion is to be formed at both axial end portions of a raw material, respectively, the following can be proposed. That is, after an enlarged diameter portion is formed at one axial end portion of the raw material, the raw material is reversed. Then, another enlarged diameter portion is formed at the other axial end portion.
In this proposed method, however, in cases where a member having enlarged diameter portions at both axial end portions (e.g., automobile arm members or automobile shaft members, or compressor double-leaded pistons) is manufactured, the number of steps for manufacturing the member increases, resulting in an increased manufacturing cost.
Furthermore, in general, according to an upsetting method, as shown in FIG. 10, unfilled portions 52 and 52 (i.e., portions where no material of the raw material 55 is filled) may generate at corner portions of the forming dented portion 51 of a female die 50 at the later stage of the processing. If such unfilled portions 52 generate, the obtained forged article becomes defective in shape (e.g., insufficient material defect), which deteriorates the value as a product. Accordingly, if the forming pressure is increased by increasing the pressing force with the punch 53 for the purposed of forcibly filling the material of the raw material 55 in the unfilled portions 52 and 52, an increased larger load will be applied to the forming dented portion 51 of the female die 50. This shortens durability of the female die 50.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.